THE JOURNAL OF
VOLUME37, NUMBER1
Organic Chemistry Q Cofiyrighl 1972 by the American C h e m d SocMlr
JANUARY 14, 1972
The Acid-Catalyzed Isomerization of Thujopsene HANSU, DAENIKER, ALANR. HOCHSTETLER, KENTKAISER,AND CARRY C. KITCHENS* Givaudan Corporation, Clifton, New Jersey
07014
Received June 17, 1971 The acid-catalyzed isomerization of (- )-thujopsene (1) under nonaqueous conditions proceeds principally via the isolable spiro olefin intermediates a- and 0-chamigrene (8 and 9) to a complex mixture of isomeric tricyclic olefins. The major component of this complex mixture is rigorously shown to be 7,10-ethano-4,4,7-trimethyl1(9)-octalin (10).
employing racemic dideuteriothujopsene (2) afforded dideuteriowiddrol (4) and dideuterated bicyclic diene 6 with the deuterium label in the final products on different carbon atoms. These authors presented a mechanism which accounted for the divergent pathways observed. Further acid treatmentl1,13 of diene d afforded a tricyclic hydrocarbon identified as 2,2,3,7tetramethyltricyclo [5.2.2.0116]undec-3-ene(7).
The tricyclic sesquiterpene (-)-thujopsene is known to occur widely in genera belonging to the natural order Cupressales. Originally isolated from Hibawood oil, it has subsequently been shown to be present also in American cedarwood oiL8 The first correct structure for thujopsene was deduced by Erdtman and Norin4 and subsequent stereospecific total syntheses5 of its racemate and evidence from chemical degradatione has confirmed the earlier4 structural assignment. The absolute configuration of (-)-thujopsene was initially assigned by Enzell' and later confirmed by Dauben and OberhanslP and the naturally occurring sesquiterpene is thus known to possess structure 1. With the structure of (-)-thujopsene well established, attention has focused on the chemistry of this unusual molecule, especially protonation with appropriate acid catalysts to the rearrangement-prone cyclopropylcarbinyl cation system. Thujopsene (1) treated with aqueous oxalic acid was reported by Nagahamagto give an unidentified hydrocarbon and widdrol (3). Dauben and Friedrich"JI1' reported that treatment of thujopsene with perchloric acid in aqueous dioxane afforded primarily widdrol (3) and a bicyclic diene identified as 1,4,11,1l-tetramethylbicyclo[5.4.0]undeca3,7-diene ( 5 ) . Subsequent isomerization studies12-'4
Recently It6 and coworkerslj have reported similar results in their studies on the perchloric acid-aqueous dioxane isomerizations of thujopsene (1) and, in addition, identified small amounts of B-chamigrene ( 9 ) and a tricyclic hydrocarbon assigned structure 10 but whose structure was not rigorously proved. We have found that the acid-catalyzed isomerization of (-)-thujopsene (1) under nonaqueous conditions affords as the major initial products the isolable spiro olefin intermediates a- and B-chamigrene (8 and 9).16317 Subsequent rearrangement affords an isomeric series of principally two tricyclic olefins which we shall here designate as olefin A and olefin B. We will discuss later the rigorous structure proof of olefin B and its formulation as 7,10-ethano-4,4,7-trimethyl-l(9)octalin (10).
(1) T. Norin, Acta Chem. Scand., 15, 1676 (1961) (2) M .Yano, J . SOC.Chem. Ind. J a p . , 16, 443 (1913); S. Uchida, ibid., 81,501 (1928). (3) J. Runeberg, Acta Chem. Scand., 14, 1288 (1960). (4) H . Erdtman and T. Norin, Chem. I n d . (London), 622 (1960); T. Norin, Acta Chem. Scand., 16, 1676 (1961): 8. Forsen and T. Norin, ibid., 15, 592 (1961). (5) W. G. Dauben and A. C. Ashcraft, J . Amer. Chem. Sac., 66, 3673 (1963); 0. Buchi and J. D. White, ibzd., 66, 2884 (1964); K . Mori, M. Ohki, A. Kobayashi, and M . Matsui, Tetrahedron, 26, 2815 (1970). (6) T.Norin, Acta Chem. Scand., 17, 738 (1963). (7) C.Enzell, %bid., 16, 1553 (1962). (8) W.G.Dauben and P . Oberhansli, J . Org. Chem., 80,3947 (1965). (9) 8. Nagahama, Bull. Chem. Soc. J a p . , 88, 1467 (1960). (10) W.G.Dauben and L. E. Friedrich, Tetrahedron Lett., 1735 (1967). (11) L. E. Friedrich, Dissertation No. 67-8559,University Microfilms, Inc., Ann Arbor, Mich. (12) Y
